1. Field of the Invention
This invention relates to a metal sintered body composite material impregnated with a light metal and having improved seizure resistance, and a method for producing the same.
2. Description of the Related Art
In the case of using light metals such as aluminum alloys, and magnesium alloys, it is general to use metal matrix composite materials including reinforcing members such as ceramic fibers, ceramic particles, and intermetallic compound particles. However, when these materials are used at elevated environmental temperatures, for example, when these materials are used as members sliding at temperatures over 200.degree. C., the above conventional metal matrix composite materials cannot prevent seizure effectively. Although a larger amount of reinforcing members can be added to the above composite materials, this causes a considerable increase in production costs and a remarkable decrease in machinability.
As an effective means for solving these problems, composite materials have been proposed which are prepared by using a porous iron base metal sintered body, impregnating the porous iron base metal sintered body with a light metal, and solidifying the light metal, as disclosed by Japanese Unexamined Patent Publication (KOKAI) Nos. 63-312947, 3-189063, and 3-189066.
More specifically, Japanese Unexamined Patent Publication (KOKAI) No. 63-312947 discloses a composite material which is prepared by employing a porous body formed of a Cu-C-Mo-Fe alloy (an equivalent of SAE86) and having interconnecting pores at a porosity of 10 to 90%, impregnating the pores of the porous body with a molten light metal, and solidifying the molten light metal.
Japanese Unexamined Patent Publication (KOKAI) No.3-189063 discloses a composite material which is prepared by employing a porous iron base metal having pore surface covered with iron sesquioxide, triiron tetroxide, ferrous hydroxide and so on, impregnating pores of the porous iron base metal with a molten light metal, and solidifying the molten light metal. This composite material is expected to prevent local cells from generating at the boundary.
Japanese Unexamined Patent Publication (KOKAI) No.3-189066 discloses a composite material which is prepared by using a porous iron base metal sintered body including at least one element of nickel (Ni), cobalt (Co), chromium (Cr), molybdenum (Mo), manganese (Mn) and tungsten (W), impregnating this porous metal sintered body with a molten aluminum alloy under a pressure of 400 to 1000 kg/cm.sup.2, and solidifying the molten aluminum alloy. This publication also discloses techniques of improving corrosion resistance and heat resistance by applying electroless plating or electrolytic plating to inner surfaces of the porous metal sintered body.
Simple impregnation of the porous metal sintered body with a light metal, however, cannot attain a sufficient seizure resistance in a high temperature range. This is because the impregnated light metal plastically flows under severe sliding conditions.
This invention has been conceived in view of the above circumstances. It is an object of the present invention to provide a metal sintered body composite material having a sufficient seizure resistance in sliding by setting the micro-Vickers hardness of a metal constituting the porous iron base metal sintered body at 200 to 800.
It is a further object of the present invention to provide a method of producing a metal sintered body composite material having a superior seizure resistance in sliding.
When used in a high temperature range over 200.degree. C., the conventional metal sintered body composite materials in which ceramic fibers or intermetallic compounds are dispersed exhibit a remarkable decrease in the hardness of a light metal and accordingly cause seizure. The present inventors have found that by enabling a metal constituting the porous metal sintered body to have a micro-Vickers hardness in the range from 200 to 800, the porous metal sintered body can easily secure a space lattice structure even at high environmental temperatures, can hold the light metal tightly, and can attain improved seizure resistance even when the light metal is softened. The present inventors have also found that by stopping employing liquid quenching which often develops gas defects because of quenching liquid remaining in pores of a porous metal sintered body, and by enabling the porous metal sintered body to be gas quenched by use of an alloying element having a high quench-multiplying factor, the micro-Vickers hardness of a metal constituting a porous iron base metal sintered body can be set at 200 to 800 owing to a hardening effect of a quenched phase attained by gas quenching and a hardening effect of carbide generation after quenched. The present inventors have completed the metal sintered body composite material of the present invention based on the above findings.